This invention relates to a rock drilling bit for a pneumatic percussion hammer.
A pneumatic percussion hammer for rock drilling normally includes a tubular housing having at its upper end a top drive sub for connection to a tubular drill rod through which air may be conducted under pressure, and having a bottom or bit drive sub in which there is engaged, with limited slidable movement, an anvil, extending upwardly from a bit head which, with the anvil, constitutes a rock drilling bit. The bit head is located below the bit drive sub, and it has a number of tungsten carbide buttons protruding from its bottom. When the hammer is in operation, the anvil is struck at high frequency by a piston reciprocated pneumatically within the housing, and at the same time the hammer is rotated, rotating the bit, the anvil of which is in splined engagement with the interior of the housing.
As the bit head is rotated at the same time as the anvil is being struck at high frequency by the piston, the torsional stress on the anvil, splined to the housing, is likely to contribute very materially to failure of the anvil. Such breakages occur fairly frequently in rock drilling pneumatic hammers, and the replacement of the rock drilling bits is very costly and time consuming. Another disadvantage of bits hitherto made is that tungsten carbide buttons are likely to be sheared off after the bit has been used for a fairly short time.
If the anvil is made separately from the bit head, having its lower end screwed into the bit head, the high frequency blows of the piston on the anvil, and the torque acting on the housing, transmitted to the anvil and to which the bit head offers resistance, may result in such stresses in the bit head that the bit head will shatter.
The present invention has been devised with the general object of providing a bit of the general type described, which is particularly sturdy, durable and trouble-free in operation.